1. Field of the Invention
The present invention relates to non-human chimeric mammals created by replacement of hematopoietic cells from a hematopoietic deficient donor mammal, optionally in which additional replacement with xenogeneic cells and/or tissue are engrafted, as well as to methods for the production and use of such mammals as animal models of human diseases and as a source of human monoclonal antibodies and cytotoxic T cells.
2. Description of the Background Art
Transplantation of human hematopoietic tissues and cells has been attempted in immune-deficient animals. Partial myeloid engraftment in the immune-deficient Bg/Nu/Xid (BNX) mouse following human bone marrow transplantation (Kamel-Reid et al (1988) Science 242:1706) and partial lymphoid engraftment following grafting of fetal liver together with fetal thymus under the kidney capsule (McCune et al (1988) Science 241:1632; EP publication No. 322,240) or peripheral blood lymphocytes (Mosier et al (1988) Nature 335:256) were achieved in the severe combined immunodeficient (SCID) mouse. In particular, it has been shown that engrafted human lymphocytes can produce antibodies to a recall antigen (Mosier (1991) Advances in Immunology 50:303) and that they can be infected with HIV (Namikawa et al (1990) J. Exp. Med. 172:1055; Mosier et al (1991) Science 251:791). While investigating the SCID mouse as a model for lymphocyte differentiation and regulation, Bosma et al (1983) Nature 301:527-530) transplanted sublethally irradiated (550 rad) BALB/c mice with SCID mouse bone marrow cells, but without success. None of the BALB/c mice showed SCID allotype. Also, it has been demonstrated that more relevant models for autoimmunity could be established in SCID mice (Lupus; Myasthenia gravis).
Although all these important applications were demonstrated, it also became apparent that the engrafted human T cells in the SCID mouse are in functional anergy and that most of their immune functions are lost, such as the ability to generate cytotoxic T lymphocytes against viral antigens or a primary antibody response. This anergy could be explained by the marked genetic disparity, which could lead to poor crossreactivity between human and mouse cytokines, homing receptors and especially the histocompatibility antigens which dominate the immune response. One potential approach which might partially overcome some of these barriers could be the use of transgenic mice carrying the appropriate human transgene, such as human HLA Class I or Class II, or human cytokines. Alternatively, the functional anergy of human T cells could be avoided if it were possible to engraft other rodents, which may present different crossreactivities, with human immune response molecules. However, such animals are, in most instances, not immunedeficient, and it is therefore important to develop a general approach for the transplantation of human hematopoietic tissues in normal rodents.
Following heavy suppression of the immune and hematopoietic systems, as with lethal total body irradiation (TBI), mice typically die within 2 weeks if additional bone marrow is not provided. Even if human stem cells could theoretically grow in such mice and reconstitute the mouse's hematopoietic system, it would be expected that their slow rate of differentiation into mature immunocompetent lymphocytes or other leukocytes would prevent them from reaching large enough numbers to protect the mice from infections. Furthermore, inadequate replenishing of hematopoietic compartments would not protect the mice from death by hematopoietic failure. On the other hand, sublethal conditioning protocols (e.g., sublethal TBI), which spare substantial numbers of hematopoietic and lymphoid cells, would enable endogenous murine cells to compete effectively with transplanted human cells, and ultimately reject the human graft.
Nakamura, T. et al. (1986) Proc. Natl. Acad. Sci. USA 83:4529-4532, described successful liver allografts established by combination with allogeneic bone marrow transplantation. Thus, liver pieces from a BALB/c mouse were accepted when transplanted under the kidney capsules of lethally irradiated C3H/H3N mice which were reconstituted with bone marrow of BALB/c mice. However, such chimeric mice were found not to be useful with transplanted hematopoietic cells without the same allotype as the transplanted liver cells, since liver pieces from C57BL/6J mouse (differing in their H-2 from the bone marrow donor) were rejected. Therefore, in this system, tolerance towards liver engrafting is confined to the strain of the bone marrow donor. It would be desirable to engraft tissue or cells from donors other than the bone marrow donor's or the recipient's endogenous bone marrow, including human xenografts, in a non-human mammal. This, however, has not been previously achieved.
The use of T cell depleted allogeneic bone marrow grafts has been found to increase the rejection of such transplants by natural killer cells and T cells. Murphy et al. (1990) J. Immunol. 144:3305-3310 disclose that the use of T cell deficient SCID mice as bone marrow cell donors for an allogeneic transplant into mice having destroyed bone marrow, resulted in markedly enhanced rejection compared to syngeneic control grafts. Accordingly, this reference teaches away from the use of immunodeficient mice as bone marrow donors to allogeneic or xenogeneic recipients having a destroyed immune system.
The use of PBL as a source of human hematopoietic cells was found to be unsuccessful in lethally irradiated mice which have natural antibodies in their serum. Only strains which were incapable of making such antibodies, due to immune deficiencies or to post-natal treatment with anti-mouse IgM, were engrafted but developed graft-versus-host disease (Huttes et al (1992) Eur. J. Immunol. 91(1):197). Accordingly, this reference teaches away from the use of human hematopoietic cells for transplantation in normal lethally irradiated rodents.
PCT publication no. WO 91/16910, published (Nov. 14, 1991), by Mayo et al. and assigned to SyStemix, Inc., discloses human monoclonal antibody production in mice. Human fetal lymphold tissue is implanted in mice followed by stimulation with an immunogen, harvesting and cloning. The human fetal lymphold tissue must be implanted into an immunocompromised mammal at a site where the tissue becomes vascularized and connected to lymphold tissue and the cells proliferate, followed by applying a stimulus to the tissue, and determining the effect of the stimulus on the response of the cells. The stimulus can be immunization with an immunogen or contact with a drug.
EP 469,632, published Feb. 5, 1992, by McCune et al. and assigned to SyStemix, Inc., discloses administration of a stimulus, able to induce a physiological response from tissue cells of a particular species, to an immunocompromised host, other than a primate, lacking at least functional T cells but including tissue cells of the species; and determining the effect of the stimulus. The tissue cells are vascularized, non-transformed solid organ tissue. Also SCID/hu mice are disclosed which are infected in the human tissue with a pathogen tropic for this tissue, wherein the solid tissue is a hematopoietic tissue, and the host is a SCID/SCID mouse. Such host can be used to evaluate the effect of drugs and vaccines, and of agents for conditions on specific tissue or the immune system. The human tissue is disclosed to remain viable for more than four weeks.
PCT publication no. W0 91/16451, published Oct. 31, 1991, by Peault and assigned to SyStemix, Inc., discloses a method for affecting the ability of human cells to produce T-lymphocytes and of progenitor cells to self-regenerate, by implanting human thymus tissue which has been depleted of lymphoid cells into an immunocompromised non-human mammal at a site where it becomes vascularized and assaying for the presence of T-lymphocytes having the desired HLA composition. The host is a SCID/SCID mouse and the thymus is fetal tissue. The cellular composition is concentrated for CD34+ cells and is implanted in the kidney capsule.
PCT publication No. W0 89/12823, published (Dec. 28, 1989) by Mosier et al and assigned to Medical Biology Institute, discloses the use of SCID mice as recipients for human immune cells or tumor cells to act as an animal model for human HIV, tumor or human immune responses. Other immunodeficient hosts are suggested, such as nude mice.
PCT publication No. WO 91/18615, published (Dec. 12, 1991), by Baum et al and assigned SyStemix, Inc., discloses the production of human peripheral blood cells in xenogeneic immunocompromised non-human mammal hosts. After introduction of human fetal bone marrow into a mammalian host, after irradiation of the host, for example, a SCID/SCID mice at 200-400 RADs as whole body or a single dose of 600 RADs after shielding of thorax and abdomen. Non-human mammals having human peripheral blood cells present as at least 2%, 5% or 15% of the total peripheral blood cells is taught.
Citation of documents herein is not intended as an admission that any of the documents cited herein is pertinent prior art, or an admission that the cited documents is considered material to the patentability of the claims of the present application. All statements as to the date or representation as to the contents of these documents is based on the information available to the applicant and does not constitute any admission as to the correctness of the dates or contents of these documents.